This invention relates to a clamping device, and more particularly to an adjustable tool holder for securing a tool to the turret of a machine tool.
Clamping devices are utilized in a wide variety of applications for clamping or fastening one member to another. One form, with which the present invention is primarily concerned, is as a tool holder assembly used for securing drills, reamers, taps and similar tools in the turrets of screw machines, lathes, or similar machine tools. These tool holders provide a mechanical device for centering and aligning the cutting tools with a work piece, and usually includes a bushing which holds the cutting tool clamped to a body member which is mounted to the turret of the machine tool.
It is desirable that a tool holder assembly be adapted to perform multiple functions when used to hold cutting tools in a machine tool. For example, when used to secure a drill bit, the bushing and drill bit must initially be permitted to float laterally and axially with respect to the axis of the body member of the tool holder assembly in order to provide accurate centering and alignment of the drill bit with a work piece. Once the drill bit is properly located, however, the tool holder assembly must also be capable of securely holding the bit and bushing against the body member without any floating action to maintain this desired position with respect to the work piece.
A multiple use tool holder assembly should also be adaptable to hold a reamer or a tap. For example, a reamer requires free axial movement when it is inserted and withdrawn from a predrilled hole in a work piece in order to properly finish the hole. In such a case the tool holder assembly must not only be capable of securely holding the reamer, but also of providing some lateral and axial floating during all phases of the tool's operation.
The prior art has provided a number of tool holder assemblies, all having certain disadvantages. In one of these arrangements, the bushing is clamped to the body of the holder by a pair of clamping bolts disposed axially on opposite sides of the bushing which extend through abutting flanges projecting from the bushing and body. However, there can be a tendency to cause a tilting of the bushing as one or the other of the bolts is tightened causing a misalignment of the tool with the work piece.
Another approach has been to use a threaded tightening collar and locking nut rotatable about the periphery of the bushing and body which clamp the bushing to the body of the holder. However, in this arrangement the rotational movement of the tightening collar can cause an undesirable rotation of the bushing.
None of the above arrangements have been entirely satisfactory, and the present invention has been developed to provide not only an improved clamping device, but also an improved tool holder having multiple uses in which the bushing when clamped to the body is not caused to shift out of position by virtue of the tightening force.